The present invention relates to glass compositions (hereinafter referred to xe2x80x9cvitreous compositionsxe2x80x9d). More specifically, the present invention relates to glass compositions that can be used as coatings for alumina substrates or other inorganic materials, as sealants, as glaze (enamel) forming pastes and other glass forming materials containing the glass compositions as the primary component for glass formation.
Glass is used as a coating for ceramic substrates, such as alumina in which a circuit is formed on the surface, or as a sealant for fluorescent tubes and the like. Previously, glass compositions containing a large amount of lead oxide (hereinafter referred to as xe2x80x9chigh PbO glass compositionsxe2x80x9d) or glass forming materials (typically, a paste-like glaze forming material) containing such compositions as the primary component were used as materials for forming glass in such applications. High PbO glass compositions have a low melting point, are easily formed into glass by glass forming processing, and have superior electrical insulation properties, thereby making high PbO glass compositions suitable for the above-described applications. For example, Japanese Laid-Open Patent Publication No. 62-207739 discloses a high PbO glass composition suitable for the above-described applications.
However, in recent years, so-called lead-free glass compositions characterized by containing substantially no lead oxide have been used instead of high PbO glass compositions, in view of increasing concerns about preventing environmental pollution and to improve workplace conditions. For example, Japanese Laid-Open Patent Publication Nos. 7-81972, 8-183632, 9-188544 and 10-236845 disclose several types of lead-free glass compositions intended for use in the above-described applications.
However, the known lead-free glass compositions disclosed in the above-noted publications do not have properties that are comparable to the known high PbO glass composition with respect to the applications of coating and sealing. For example, the known lead-free glass compositions generally have firing temperatures (typically about 900xc2x0 C.) that are higher than the high PbO glass compositions. If the surface of an object (e.g., a ceramic circuit board) is glass-coated with such a lead-free glass composition, it is necessary to fire the object at a relatively high temperature after the lead-free glass composition (typically a glaze forming material prepared in the form of paste) is applied to the object. Therefore, the high temperature during firing may adversely affect the properties of the object.
It is an object of the present invention to provide glass compositions that can be used in applications such as coating ceramic substrates, e.g., alumina, or sealing fluorescent tubes or the like under the same conditions that were used for the known high PbO glass compositions and without containing a large amount of lead (typically lead-free); glass forming materials containing such glass compositions as the primary component for glass formation are also provided.
Glass compositions provided by the present invention comprise primary oxide components in an amount of 85% (by weight, which applies to the following discussion) or more (preferably 90% or more) of the total weight of the composition; the primary oxide components include ZnO, B2O3 and P2O5 as essential components and the primary oxide components are provided in the amounts of 50 to 80% of ZnO, 5 to 35% of B2O3, 1 to 20% of P2O5, 0 to 10% of Al2O3, 0 to 15% of MgO, 0 to 10% of CaO, and 0 to 5% of BaO.
Additional glass compositions provided by the present invention include glass compositions that are substantially free of lead oxide and comprise primary oxide components in an amount of 90% or more (preferably 95% or more) of the total weight of the composition; the primary oxide components include ZnO, B2O3 and P2O5 as essential components and the primary oxide components are provided in the amounts of 45 to 80% of ZnO (preferably, 45 to 75% of ZnO), 5 to 45% of B2O3, 1 to 35% of P2O5, 0 to 10% of Al2O3, 0 to 15% of MgO, 0 to 10% of CaO, and 0 to 5% of BaO.
Glass compositions having these formulations (e.g., oxide glass compositions substantially comprising only vitreous oxide components) do not require excessive care to prevent environmental pollution, unlike the high PbO glass compositions. Furthermore, the firing temperature can be set to a temperature lower than known lead-free glass compositions (e.g., 650xc2x0 C. or less). Therefore, it is possible to prevent property degradation of an object subjected to a glass coating process, such as a ceramic substrate, due to high firing temperatures. Preferably, the sum of the weight percentages of Al2O3, MgO, CaO and BaO in the glass compositions of the present invention is 15% or less (more preferably, 10% or less) of the total weight of the primary oxide components.
Additional preferred glass compositions of the present invention comprise primary oxide components in the amounts of 50 to 65% of ZnO, 10 to 30% of B2O3, and 10 to 30% of P2O5 (provided that the sum of the weight of B2O3 and P2O5 is 30 to 45% of the total weight of the composition); in addition, the glass compositions include 0 to 15% of one or two or more oxides selected from the group consisting of Al2O3, MgO, CaO, and BaO (provided that the weight percentage of BaO is 0 to 5% of the total weight of the primary oxide components). Such glass compositions can realize improved glass formation at comparatively low firing temperatures.
Another preferred glass composition of the present invention is an oxide glass composition that substantially comprises said primary oxide components in any of said weight proportions (the presence of a trace amount of impurities on the order of less than 1% is allowable).
Other preferred glass compositions of the present invention are substantially free of SiO2 or only include SiO2 in an amount of less than 1% of the total weight of the composition. Glass compositions that are free of SiO2 or contain an extremely low amount of SiO2 are preferable, because such glass compositions rarely devitrify during glass formation.
Other preferred glass compositions of the present invention are substantially free of alkali metal oxides and alkali metal ions (i.e., these substances are not present at all, or if present, the amount thereof is only in an unavoidable level as impurities or in a trace amount that does not affect glass formation, which also applies to the following discussion). Glass compositions having such a constitution enable prevention of beforehand damages to a circuit due to migration of alkali metal ions after a ceramic substrate circuit board has been subjected to glass coating. Therefore, circuit boards or the like that have been subjected to glass coating can be made more reliable and durable.
Furthermore, the present invention can provide glaze forming pastes or other glass forming materials containing the glass compositions of the present invention as a primary component for glass formation.
For example, glass forming materials comprising a glass composition as a glass forming component are provided; the glass composition comprises primary oxide components in an amount of 85% or more (preferable 90% or more) of the total weight of the composition; the primary oxide components include ZnO, B2O3 and P2O5 as essential components and the primary oxide components are provided in the amounts of 50 to 80% of ZnO, 5 to 35% of B2O3, 1 to 20% of P2O5, 0 to 10% of Al2O3, 0 to 15% of MgO, 0 to 10% of CaO, and 0 to 5% of BaO. In the alternative, glass forming materials comprising a glass composition as a glass forming component are provided, in which the glass composition is substantially free of lead oxide and comprises primary oxide components in an amount of 90% or more (preferably 95% or more) of the total weight of the composition; the primary oxide components include ZnO, B2O3 and P2O5 as essential components and the primary oxide components are provided in the amounts of 45 to 80% of ZnO (preferably 45 to 75% of ZnO), 5 to 45% of B2O3, 1 to 35% of P2O5, 0 to 10% of Al2O3, 0 to 15% of MgO, 0 to 10% of CaO, and 0 to 5% of BaO. These glass forming materials enable sealing and coating processes at firing temperatures that are lower than glass forming materials comprising the known lead-free glass composition as the primary component.
Preferred glass forming materials comprise the glass composition in the form of a powder and an appropriate vehicle and are prepared as a paste. Such paste-like materials are suitable for forming a glass layer (glaze) on the surface of various ceramic products (substrates, etc.).